To improve the practical application of the thermal expansion of closed long pipeline exposing to external heating sources such as solar energy, safety engineering and system optimization for relief valve in the closed piping system are suggested through theoretical approach, correlation in view of temperature and pressure increase caused by external solar energy in the closed piping system. The profile for thermal relief valve including relieving capacity, influx heat energy, sizing criteria, set pressure, selection against back pressure is also presented. It is noted that following topic on solar relief valve should be applied to engineering, installation and commissioning.